Annular catalytic converter

ABSTRACT

The invention relates to an annular catalytic converter, having a first, tubular flow path, having a diverting region ( 4 ) and having a second, annular flow path, wherein the tubular flow path is formed by an inner pipe ( 1 ), wherein the annular flow path is formed between the inner pipe ( 1 ) and an outer pipe ( 2 ) surrounding the inner pipe, and the diverting region ( 4 ) is of pot-shaped form for the purposes of diverting the exhaust-gas flow from the tubular flow path into the annular flow path, wherein the inner pipe ( 1 ) and/or the outer pipe ( 2 ) has a conical cross section (D 1 , D 2 , D 1 , D 4 ) that widens or narrows along the flow direction of the exhaust gas.

TECHNICAL FIELD

The invention relates to an annular catalytic converter, having a first, tubular flow path, having a diverting region and having a second, annular flow path, wherein the tubular flow path is formed by an inner pipe, wherein the annular flow path is formed between the inner pipe and an outer pipe surrounding the inner pipe, and the diverting region is of pot-shaped form for the purposes of diverting the exhaust-gas flow from the tubular flow path into the annular flow path.

PRIOR ART

So-called annular catalytic converters are used for the purposes of exhaust-gas aftertreatment in particular when the available installation space is limited and it is nevertheless sought to achieve as long a flow path as possible within the catalytic converter.

An annular catalytic converter has a central tubular flow path. The exhaust gas flows out of the tubular flow path into a diverting chamber, which effects a diversion of the exhaust gas outward in a radial direction and finally diverts the exhaust gas such that it flows, oppositely with respect to the flow direction in the tubular flow path by 180 degrees, through an annular flow path. Here, the tubular flow path and the annular flow path may for example be arranged concentrically with respect to one another. The annular flow path is delimited to the inside by the wall of the tubular flow path and to the outside by an outer pipe and/or a jacket.

Annular catalytic converters are used in particular in turbocharged internal combustion engines, directly downstream of the turbocharger. For optimum functioning of the catalytically active carrier matrices arranged in the annular flow path, the most uniform possible distribution of concentration and flow is advantageous.

A disadvantage of the devices from the prior art is in particular that no optimum uniform flow distribution and uniform concentration distribution are achieved at the catalytically active support matrices, resulting in non-optimal exhaust-gas aftertreatment.

Presentation of the Invention, Problem, Solution, Advantages

The problem addressed by the present invention is therefore that of creating an annular catalytic converter which generates the most optimum possible uniform flow distribution at the inlet cross section of the catalytically active matrices.

The problem is solved with regard to the annular catalytic converter by means of an annular catalytic converter having the features of claim 1.

One exemplary embodiment of the invention relates to an annular catalytic converter, having a first, tubular flow path, having a diverting region and having a second, annular flow path, wherein the tubular flow path is formed by an inner pipe, wherein the annular flow path is formed between the inner pipe and an outer pipe surrounding the inner pipe, and the diverting region is of pot-shaped form for the purposes of diverting the exhaust-gas flow from the tubular flow path into the annular flow path, wherein the inner pipe and/or the outer pipe has a conical cross section that widens or narrows along the flow direction of the exhaust gas.

The inner pipe and the outer pipe may be arranged concentrically with one another or offset with respect to one another. The concentric arrangement is advantageous in order, in particular along the tubular flow path, to generate cross sections which in each case remain constant along the circumference.

Owing to the conicity of the inner pipe and/or of the outer pipe, various combinations can be generated which, for example, lead to a tubular flow path that narrows or widens in the flow direction of the exhaust gas. The annular flow path may also narrow or widen in the flow direction of the exhaust gas. In a special configuration, the ring-shaped flow path may have a cross section that remains constant even in spite of the conical inner pipe and the conical outer pipe.

It is particularly advantageous if the inner pipe has a cross section that widens conically in the flow direction of the exhaust gas and the outer pipe has a cross section that narrows in the flow direction of the exhaust gas.

The conical widening of the inner pipe can in particular improve the efficiency of an upstream turbocharger, because the enlargement of the cross section in the flow direction allows dynamic pressure to be converted into static pressure. This contributes to an improved effect of the turbocharger, whereby ultimately the efficiency of the internal combustion engine driving the turbocharger can be improved.

The conical design of the outer pipe is advantageous in order to adapt the ratios of the cross-sectional areas from the gas inlet side of the annular flow path to the gas outlet side of the annular flow path such that differences in prestress in the matrix arranged in the annular flow path can be compensated. In this way, it is possible to prevent cell deformations in the matrix, and furthermore the undesired occurrence of holes or openings in the matrix. Overall, it is thus possible in particular for the longevity of the annular catalytic converter to be significantly improved.

It is also advantageous if the inner pipe and/or the outer pipe has an oval or an elliptical cross section. Oval or elliptical cross sections may be advantageous in particular in the case of restricted installation space conditions. In this way, in the case of little installation space being available, the largest possible volume of the catalytic converter and in particular of the catalytically active matrices can be achieved.

A preferred exemplary embodiment is characterized in that the inner pipe and the outer pipe have the length (L) and the tubular flow path has a cross-sectional area (D1) at its gas inlet side and the annular flow path has a cross-sectional area (D2) at its gas outlet side, wherein the tubular flow path widens conically from its gas inlet side to its gas outlet side with the angle (α1) and the annular flow path narrows conically from its gas inlet side to its gas outlet side with the angle (α2).

Assuming identical angles of α1 and α2, this generates walls of the inner pipe and of the outer pipe which run parallel to one another. If the angles α1 and α2 are configured to differ, this thus also results in a conically narrowing or widening annular flow path.

It is also preferable if a particularly preferred size ratio of the annular catalytic converter is defined by the formula

${\tan({\alpha 2})} = \frac{\sqrt{{D\; 2^{2}} - {D\; 1^{2}} + \left( {{D\; 1} + \left( {L*{\tan({\alpha 1})}} \right)^{2}} \right.} - {D\; 2}}{L}$

A design of the annular catalytic converter in accordance with the above formula yields an optimum result with regard to the prestress conditions in the annular catalytic converter, because a very homogeneous stress state can be achieved. This is in particular owing to the size ratios of the cross-sectional areas, of the lengths and of the cell sizes of the matrices used.

It is furthermore advantageous if at least one matrix formed by a metallic honeycomb body is arranged in the annular flow path, wherein the matrix has a cross-sectional profile that follows the cross-sectional profile of the annular flow path. Depending on the application, a multiplicity of matrices may also be provided, which have different coatings in order to convert different constituents of the exhaust gas.

It is furthermore advantageous if the metallic honeycomb body is formed by a multiplicity of metallic foils which are stacked one on top of the other and which are wound up to form the honeycomb body, wherein at least some foils are corrugated, wherein the conicity of the metallic honeycomb body and thus of the matrix along its flow direction can be influenced through variation of the corrugation height and of the corrugation density between the gas inlet side and the gas outlet side of the matrix. Metallic honeycomb bodies can be specially adapted in order to adapt them to the spatial conditions. In particular to avoid undesired flows around the honeycomb bodies, it is advantageous if the honeycomb body is adapted to the geometry of the flow path and terminates flush with the walls of the flow path. The generation of conical honeycomb bodies is known and can be achieved in particular by way of the measures mentioned above.

It is also expedient if the diverting region has a cooling device. For example, the cooling device may be formed by a double-walled section, which can be flowed through by a coolant, of the diverting region. This double-walled section may be formed in certain regions or throughout the entire diverting region. For example, double-walled sections may also be formed by channels which are formed in the wall of the diverting region and which can be flowed through by a coolant. The throughflow may be regulated for example by means of a wastegate or a bimetal.

Alternatively, the cooling device may be formed by a cooling coil arranged at or in the diverting region. A cooling coil is formed by a closed volume, for example a hose or a pipe, which can be flowed through by a coolant, and may be arranged at the locations to be cooled. The cooling device may additionally have ribs which project into the diverting region or which project outwardly away from the diverting region.

As a result of the cooling of the diverting region, it is possible to operate with the combustion air ratio of λ=1 for longer, and thus to reduce the exhaust-gas emissions. This is because, as a result of the cooling, the exhaust-gas mass flow upstream of the catalytically active matrix is cooled such that, at high load points of the internal combustion engine, it is possible to operate with λ=1 for longer without the temperatures of the exhaust gas and of the affected components becoming too high and the structural integrity of the annular catalytic converter being jeopardized.

Furthermore, as a result of the cooling of the diverting region, the viscosity of the exhaust-gas flow in the region close to the wall can be reduced. As a result of a lowering of the viscosity and thus of the resulting friction, the pressure loss that occurs in the throughflow can be reduced.

It is particularly advantageous if the inner pipe has, at the gas outlet side of the tubular flow path and at the gas inlet side of the annular flow path, a guide element by means of which the exhaust-gas flow flowing through the annular catalytic converter is diverted. By means of a guide element, the flow, which is diverted in the diverting region after flowing through the gas outlet side of the tubular flow path and before flowing through the gas inlet side of the annular flow path, can be diverted into a certain direction, and the mixing of the gas flow can be influenced. A guide element may be designed as an additional component which is arranged on one of the inner walls, or may also be an integral part of one of the walls.

It is also advantageous if the guide element is generated by a bead-like bend of the free end of the inner pipe radially outward and into the annular flow path. This is particularly advantageous because no additional components are required, and the production process is thus particularly simple. In particular, bends with a particularly small radius, which could result in the generation of separation edges that can adversely affect the flow of the exhaust gas, are avoided by means of a bead-like bend.

It is also preferable if an optimized incident flow onto a matrix arranged in the annular flow path is achieved by means of the inner wall of the diverting region in conjunction with the guide element on the inner pipe. This is advantageous in particular in order to achieve as homogeneous a flow distribution as possible and as homogeneous a concentration distribution as possible over the cross-sectional area of the catalytically active matrix.

Advantageous developments of the present invention are described in the dependent claims and in the following description of the figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be discussed in more detail below on the basis of exemplary embodiments with reference to the drawings. In the drawings:

FIG. 1 shows a schematic view of the inner pipe and of the outer pipe of an annular catalytic converter for the purposes of illustrating the different cross-sectional areas and angles,

FIG. 2 shows a schematic sectional view through the annular catalytic converter, wherein the diverting region is of double-walled design and can be flowed through by a coolant, and

FIG. 3 shows a detail view of the diverting region and of the guide element formed on the inner pipe.

PREFERRED EMBODIMENT OF THE INVENTION

FIG. 1 shows a schematic view of the inner pipe 2, which is surrounded by the outer pipe 2. The two pipes 1 and 2 are oriented concentrically around the central axis 3. The cross-sectional area D1 is shown at the gas inlet side of the inner pipe 1, whereas the cross-sectional area D3 is illustrated at the gas outlet side of the inner pipe 1. The cross-sectional area D4 or the differential area A2 between the cross-sectional areas D3 and D4 is shown at the gas inlet side of the annular flow path which is formed between the inner pipe 1 and the outer pipe 2. The differential area A1 between the cross-sectional areas D1 and D2 is shown at the gas outlet side of the annular flow path.

The inner pipe 1 widens from the gas inlet side to the gas outlet side by the angle α1 with respect to the central axis 3. The outer pipe widens from its gas outlet side to its gas inlet side by the angle α2 with respect to the central axis.

The throughflow sequence is from the gas inlet side of the inner pipe 1 to the gas outlet side of the inner pipe 1, where, in the diverting region not shown in FIG. 1, the exhaust gas is diverted into the gas inlet side of the outer pipe 2 or of the annular flow path. From there, the exhaust gas flows to the gas outlet side of the annular flow path or of the outer pipe 2.

The pipes 1, 2 have a length L which, in the exemplary embodiment in FIG. 1, is identical for both pipes 1, 2.

A variation of the angles α1 and α2 leads to different geometries for the tubular flow path and the annular flow path. In particular, the annular flow path may have a cross section that remains constant along the flow direction, or a varying cross section.

FIG. 2 shows a view of the gas outlet side of the tubular flow path, and the diverting region 4 adjoining said gas outlet side. The diverting region 4 is formed by a pot-shaped wall 5, which serves as a baffle wall for the inflowing exhaust gas and which ultimately serves to divert the exhaust gas outward in a radial direction and ultimately into the annular flow path.

As can be seen from the arrows in FIG. 2, the main flow direction in the tubular flow path is opposite to the main flow direction in the annular flow path.

Also shown is a second wall 6, which follows the profile of the inner wall 5 and which thus forms a region 7 through which flow can pass, for example a channel or some other closed volume through which flow can pass. This can be flowed through by a coolant, and thermal energy can thus be dissipated from the exhaust gas via the inner wall 5.

The free end of the inner pipe 1 furthermore has a bead-like bend radially outward and into the annular flow path. This generates the guide element 10, which is intended to improve the exhaust-gas flow in the volume 9 enclosed by the diverting region 4. The guide element 10 is configured to be of fully encircling form in a radial direction.

FIG. 3 shows a detail view of the diverting region 4 and in particular of the size ratios of the inner wall 5 and the guide element 10 in relation to the diameter D of the tubular flow path at its gas outlet. A diverting region 4 and a guide element 10 which have dimensions within the magnitudes specified in the table below are particularly advantageous in order to generate the most homogeneous flow possible at the gas inlet of the annular flow path or of the catalytically active matrix 8.

0.0153 ≤ R1/D ≥ 3.450 0.0153 ≤ R2/D ≥ 3.461 0.0076 ≤ R3/D ≥ 3.461 0.0076 ≤ R4/D ≥ 3.461 0.0153 ≤ R5/D ≥ 3.461 0.0153 ≤ R6/D ≥ 3.461  1.100 ≤ D7/D ≥ 3.461 0.0153 ≤ L1/D ≥ 3.384 0.0076 ≤ L2/D ≥ 3.384 0.0153 ≤ L3/D ≥ 3.384 0.0153 ≤ L4/D ≥ 3.438 0.0153 ≤ L5/D ≥ 3.438 0.0000 ≤ L6/D ≥ 3.469 0.0153 ≤ L7/D ≥ 3.4446 0.0153 ≤ L8/D ≥ 3.450 0.0153 ≤ L9/D ≥ 4.230 0.0460 ≤ L10/D ≥ 3.461 0.0460 ≤ L11/D ≥ 3.461 0.0460 ≤ L12/D ≥ 3.461 0.0153 ≤ L13/D ≥ 3.461 0.0153 ≤ L14/D ≥ 3.461 0.0153 ≤ L15/D ≥ 3.461

Here, the free end of the inner pipe is bent outward and does not come back into contact with the outer side of the inner pipe. Here, the reference designations L1 to L15 each denote lengths of individual sections. The reference designations R1 to R6 denote different radii of the components. The reference designation D denotes the diameter of the inner pipe at its gas outlet side and the reference designation D7 denotes the diameter of the outer pipe at its gas inlet side.

The different features of the individual exemplary embodiments can also be combined with one another. The exemplary embodiments in FIGS. 1 to 3 are in particular not of a limiting nature and serve for illustrating the concept of the invention. 

1. An annular catalytic converter, having a first, tubular flow path, having a diverting region (4) and having a second, annular flow path, wherein the tubular flow path is formed by an inner pipe (1), wherein the annular flow path is formed between the inner pipe (1) and an outer pipe (2) surrounding the inner pipe, and the diverting region (4) is of pot-shaped form for the purposes of diverting the exhaust-gas flow from the tubular flow path into the annular flow path, characterized in that the inner pipe (1) and/or the outer pipe (2) has a conical cross section (D1, D2, D3, D4) that widens or narrows along the flow direction of the exhaust gas.
 2. The annular catalytic converter as claimed in claim 1, characterized in that the inner pipe (1) has a cross section (D1, D3) that widens conically in the flow direction of the exhaust gas and the outer pipe (2) has a cross section (D4, D2) that narrows in the flow direction of the exhaust gas.
 3. The annular catalytic converter as claimed in any one of the preceding claims, characterized in that the inner pipe (1) and/or the outer pipe (2) has an oval or an elliptical cross section.
 4. The annular catalytic converter as claimed in any one of the preceding claims, characterized in that the inner pipe (1) and the outer pipe (2) have the length (L) and the tubular flow path has a cross-sectional area (D1) at its gas inlet side and the annular flow path has a cross-sectional area (D2) at its gas outlet side, wherein the tubular flow path widens conically from its gas inlet side to its gas outlet side with the angle (al) and the annular flow path narrows conically from its gas inlet side to its gas outlet side with the angle (α2).
 5. The annular catalytic converter as claimed in claim 4, characterized in that a particularly preferred size ratio of the annular catalytic converter is defined by the formula ${\tan({\alpha 2})} = \frac{\sqrt{{D\; 2^{2}} - {D\; 1^{2}} + \left( {{D\; 1} + \left( {L*{\tan({\alpha 1})}} \right)^{2}} \right.} - {D\; 2}}{L}$
 6. The annular catalytic converter as claimed in any one of the preceding claims, characterized in that at least one matrix (8) formed by a metallic honeycomb body is arranged in the annular flow path, wherein the matrix (8) has a cross-sectional profile that follows the cross-sectional profile of the annular flow path.
 7. The annular catalytic converter as claimed in claim 6, characterized in that the metallic honeycomb body (8) is formed by a multiplicity of metallic foils which are stacked one on top of the other and which are wound up to form the honeycomb body (8), wherein at least some foils are corrugated, wherein the conicity of the metallic honeycomb body (8) and thus of the matrix (8) along its flow direction can be influenced through variation of the corrugation height and of the corrugation density between the gas inlet side and the gas outlet side of the matrix (8).
 8. The annular catalytic converter as claimed in any one of the preceding claims, characterized in that the diverting region (4) has a cooling device (5, 6, 7).
 9. The annular catalytic converter as claimed in claim 8, characterized in that the cooling device (5, 6, 7) is formed by a double-walled section (5, 6, 7), which can be flowed through by a coolant, of the diverting region (4).
 10. The annular catalytic converter as claimed in either one of the preceding claims 8 and 9, characterized in that the cooling device is formed by a cooling coil arranged at or in the diverting region.
 11. The annular catalytic converter as claimed in any one of the preceding claims, characterized in that the inner pipe (1) has, at the gas outlet side of the tubular flow path and at the gas inlet side of the annular flow path, a guide element (10) by means of which the exhaust-gas flow flowing through the annular catalytic converter is diverted.
 12. The annular catalytic converter as claimed in claim 11, characterized in that the guide element (10) is generated by a bead-like bend of the free end of the inner pipe (1) radially outward and into the annular flow path.
 13. The annular catalytic converter as claimed in any one of the preceding claims, characterized in that an optimized incident flow onto a matrix (8) arranged in the annular flow path is achieved by means of the inner wall (5) of the diverting region (4) in conjunction with the guide element (10) on the inner pipe (1). 